This invention relates to a storage medium utilized as an external storage unit of a computer and more particularly to a method of managing data in a storage medium having a latency time and seek time which affect access speed.
In the past, a rewritable magnetic storage medium such as an floppy disc has been utilized as external storage unit but recently a write-once type medium such as in write-once type optical disc has been gaining a use. Especially, in this type of portable medium, information necessary for managing data in the medium is often recorded, along with the data, on the storage medium to take advantage of portability of the medium.
Concomitantly with renewal of data such as addition of data, management information associated with the data is renewed frequently and if the medium is rewritten with the whole of the renewed management information each time renewal occurs, efficiency of use of the capacity of the medium will be degraded. As a countermeasure, a management system is generally used in which upon renewal of management information, only renewal history information indicative of the changed contents or differential information representative of a renewed portion is recorded on the medium and is read, during initialization in the event of exchange of the medium, from the medium so as to reconstruct the latest management information in an internal storage (a memory or a memory used in combination with an auxiliary storage medium) by looking up the contents of the renewal history information or the differential information.
Occasionally, the above management system may also be applied to, in addition to the write-once type medium, a medium such as a rewritable optical disc which tends to degrade through frequent rewriting. Examples of management schemes using the renewal history information described above will now be discussed for reference purposes.